Automatic frequency control system for braking-field oscillators



Sept. 1,6, 1941- R.v w. GEORGE 2,256,083

AUTOMATIC FREQUENCY CONTROL SYSTEM FOR BRAKING-FIELD OSCILLATORS FiledApril l5, 1959 3 Sheets-Sheet l AAA.. .Alim -v v n... vvvv vvL`,Wolff/M4 T 7 g 116 Wg/00 TUBE PHASE ADJusrER COU/L ING BAR/am us5/vosC/M701?- DETECTOR INVENTOR.

I ,QA Hu/.GEORGE BY ATTORNEY.

Sept. l

R; W. GEORGE AUTOMATIC FREQUENCY CONTROL SYSTEM FOR BRAKENG-FIELDOSClI-.ILATORS DIFFERENT/.4L DETECTOR DE TECTOR v PHASE AoJusrER FiledApril l5, 1959 3 Sheets-Sheet 2 NA m E N |H||,

4H ES? f 35 ....E V "Il" qc, 5% v l||||||||||| LL Si Q ATTORNEY.

Sept. 16, 1941. R, w. GEORGE 2,256,083

AUTOMATIC FREQUENCY CONTROL SYSTEM FOR BRAKING-FIELD OSClLLTORS FiledApril l5, 1939 3 SheehS-Shet 5 BAR/(HA l/SEN asc/mme IZQ 3 acAMpL/F/ER 4Z L /NTEpMEo/ATE FREQUENCY Dgff/OZAL l AMPL/F/ER g U5 ULTRA H/GH/NTEnMEU/ATE FREQUENCY FREQUENCY D/SQETRE/TTOL AUD/0 asc/Mrap AMPM/VEROUTPUT E19, 4 1 u l/ TRANS ULTRA f//GU FREQ.

asc/wrok DIFFERENT/AL oETEcToR A HI +Ep A ac AMpL/F/ER .5

. ELECT/MAGNET v o/FFEEENT/AL l NEAR U50. TUBE UETECTUR -l- L Y gINVENTOR.

- ATTORNEY.

UNITED; stares are `mrroiulrrio FREQUENCY ooNTnoL sys- TEM FoaBaarnse-rieti) osciLLA'roits Ralph W. George, Riverhead, N; Y., assignerto Radio Corporation of America, a corporation of Delaware 'y @ENCE AApplication April 15, 1939, Serial No. 268,014

1 Claim. (Cl. Z50-Bil) The present invention concerns an ultra highbodying the principles of rthe present invention; frequency oscillatorsystem, such as a braking Fig. 5a shows schematically anelectromechanield or Barkhausen-Kurz type, whose frequency cal circuitarrangement whichv can be used for can be automatically controlled byvarying the some of thecircuits of Fig. 4; andrFigp5b shows voltages ofthe oscillator or by the tuning of the a modified circuit which can beused for electrooscillator circuit. According to the invention, amagnetic control of the oscillator. The same diiferential detectoroperates at a suitable inreferencennumerals appearing throughout thetermediate frequency and sets up a plus or minus figures of the drawingsdesignate the same or voltage which is amplified suitably and made toequivalent parts.

control the grid or plate voltage, or the tuning lo Therterm Barkhausenis herein used broadly of the ultra high frequency oscillator in a manasbeing descriptive of any typeof electron disner to compensate for achange in the intercharge device using a grid which is maintainedmediate frequency. Where it is desired to conata high positive.potential anda plate or anode trol a receiver, it is proposed to makethe ultra at. a much lower potential with Yrespect to the high frequencyoscillator follow the transmitter l5 cathode, whereby oscillations ofelectrons about frequency. Where it is desired to control a the gridmayor may not bemade to'occur, detransmitting ultra. high frequencyoscillator, it pending upon the adjustment of the circuit conis proposedto combine a relatively weakultra stants and voltages.

high frequency of known stable frequency such Referring to Fig.. 1ofthedrawings, there is as a harmonic of a local stable oscillator, or2O shown an ultra short radio wave fr'equelly-IlflOll-l crystalcontrolled oscillator with the transmitulation receiver having adifferential detector and ter frequency to produce a suitableintermediate a direct current amplier stage which gives a voltfrequencywhich through the diiferential detecage output carrying plus or minuswith theintertor produces suitable controlling means which mediatefrequency. More specifically, the circuit are applied to the ultra highfrequency transmit- 0f Fig- 1 ShOWS 2, receiving antenna Of the die tingoscillator. pole type which is coupled by means of a trans- It is knownthat ultra high frequency oscillators mission line to the Lecher wiresystem 2 conare especially subject to slight and uncontrollable nectedin turn to the grid 3 and anode 4 0f a variations in their circuitconditions, etc., which Barkhausen oscillator-detector 5,. The Lechercause frequency variations, and it is also known 30 Wle SyStBmSShllllted by a COIldGIlSer 6 and an to use crystals as frequencystabilizing elements. additional tunable condenser l, the latter beingDirect crystal control of the frequency of the osutilized for tuning theresonant period of the oscillator through many stages of frequencymulticillator detector circuit. Condenser 9 serves to plication,however, is complicated and expensive, ground the plate orranode 4 ofthe Brarkhausen and therefore not well suited for reception purdetector5 for radio frequency potential. Batposes and most transmissionpurposes. teries B4 and B5 provide suitable pOlaIiZiIlg D0- The presentinvention is a means of obtaintentials to the plate ll and grid 3,respeCtiVQly, ing automatic frequency control with a moderate of thevacuum tube 5. The grid 3 is maintained amount of apparatus, which hasan advantage at a high positive potential by a battery B5; and that itwill keep a receiver in tune with a transthe P12308 4 al? an extremely10W POStVe 0I' nega'- mitter over a long period of time and without tivepotential with respect to the cathode Il).

attention. v The intermediate frequency which is produced Anotheradvantage 0f the invention is that the by combiningthe signal andoscillator frequenfrequency control achieved requires only a very ciesin detector 5 is taken from the grid side of small amount of power fromthe stable oscil- 3 the Lecher wire system2`and is coupled throughlater, when applied@ frequency @enum of e, transformer Il tointermediate lfrequency amplitransmitter oscillator. iierv l2, theoutput of which vis passed to the A further and important advantage ofthe ingrid of the coupling tube I3. A condenser lill) is vention is thatconstant frequency or tuning is used to tune the primary coil oftransformer Il maintained regardless of any ordinary voltage 50 to thedesired intermediate frequency. The outchanges to any of the componentparts. put of the coupling tube I3 is passed to a phase A description ofthe invention follows in conadjustment circuit I4, the latter 0f whichmay junction with drawings, wherein Figs. l to 4, be enclosed in ashield. Although not shown in inclusive, illustrate four different'embodiments the drawings, it should be understood that all of an ultrahigh frequency oscillator system em- 53 radio frequency circuits areproperly shielded in conventional manner. The phase adjuster I4 may takeVthe form' of an artificial line. The signal energy derived from thephase adjuster'is resonated in parallel tuned circuit I5, in turncoupled'to parallel tuned circuit I6, the latter being connected betweenthe grids of balanced modulator detectors I1 and I 8. The detectors I'IandA [8f comprise a differential detector circuit whose purpose will begiven later. Ther same signal energy applied to the grid of the couplinganode current of one tube I'I or I8 of the 'Y Vdifferential detectorwill increase While that of theother tube I8 or I 'I Will decrease, withtube I3 is also applied through connection I9 to Vthe .grid of the phaseshiftrlr transformer cou:

pling tube 20, from whose anode cophasal signal potentials are fed tothe cathodes of the differential detectors II and I8,- asshown. It willthus be appreciated that a diierential signal is applied to the grids ofthe detectors I I and I8 while a cophasal signalis appliedto thecathodesof these detector tubes. This portion of the frequency modulationreceiver comprising the stages I 2 to. 20 is Yvery similar to and`adequately de,.- .sripeu inf my. United, ,States .Patent No. 2.03.5345,erantedJMareh 3,1; 1.936. particularly Fig. 2, te

' `which reference is hereinmadefor amore d etailed description thereof.Coupled across the anodes ofv the differential detector' I'I and I8there isprovided a direct current amplifier stage 27| whichappliesapcontrol voltage tothe plate 4 of the BarkhausenV oscillator detectortube 5.over

- connection 22. which includes inl series therewith bat-terr B3. andpart of battery B4. The battery 3.3.?. Supplies plate power to thedirect current amplifier 2l 'while the battery B is used Yto reduce theplate voltagev of the direct current amplifier 2l to a, value moresuitable for use in circuit with the plate ofv the Barkhausen,oscillator 5. The battery- B I serves to apply. positive polarizingpotentials to fthe` mid point ofthe potentiometer resistor RI, R2, theresistors o f whichare serially connected. Withrespect to each other andin shunt to the 'output of the differential detector I'I, I 8.

` 'l suitable audio frequency output circuit, 34 is shownl coupledAthrough an audio output transformer 23, tofthe anodes of thedifferential detector I1, I8.V Connections suitable for receivingamplitude orffrequency modulation areobtained byemploying a reversingswitch 2,4 yin one section of the primary winding of the audio frequencytransformer, as shown, Element 25 comprises a suitable head phone Vorother signal utilization means. A suitable low, pass (audio frequency)Viilterpas.. shown, serves tofpass only loW frequency variations of the.direct current control voltage tothe rst heterodyne oscillator.

In thev operation of Fig. l, the receiver functionssubstantially.identically with the frequency modulationkreceiver described in myabove'men- Y tioned United States Patent No.-2,035,7,45 .withV thefollowing differences. 'The anode current of` the two vacuumtubes I ,1.and i8, Of thediieren` ,3.

tial Cli'aeotor is passed through the potentiometer branches Rl and. R2,respectively, before being connected with the detector plate supply Bl.The voltages across. the resistances RI andv R2r are egual and-oppositeas long asthe signal intermediate frequeney'is et vthe mid band 0f thedetector, ,asV isalsothe case When-no signal is present.' Normally, theresultant voltage Ec acrossthe grid land cathode of the direct currentamplifier 2ll iszero, and. thevoltageacross the anode impedance,R3-isconstant,v andthe plate voltage of the Barlgliausen-oscillator isconstant.

the result that the Voltage Ec impressed on the direct current amplifier2| Will be changed, in turn producing a change in the voltage across R3which is impressed on the plate 4 of the Barkhausen oscillator 5. Thepolarity of the poten tial Ec is so chosen that the resulting voltage'onthe plate of the Barkhausen oscillator 5 will change the frequency ofthe oscillator in a direction to bring the intermediate frequency backto the mid'band of the differential detector.

Fig. 2 shows a modification of Fig. 1 in that the automatic frequencycontrolling voltage from the differential detector is applied both tothegrid 3 and to the plate 4 of the Barkhausen oscillatordetector 5,although it will be appreciated that if desired this controlling voltagemay be applied only to the grid of the Barkhausen detector. In Fig. 2,there is also provided a dilerential direct current amnlier Comprisingvacuum tubes 25, 2.1 for producing differential Changes in the plete andgrid voltages of theBarkhausen oscillator' 5, The circuitl arrangementVhere used for supplying the differential voltage Ec to the differentialv'clip-v rect current amplifier eliminates the Vnecessity for the lowfpass filter of Fig. 1. 1nv operation, onehalf the voltage across`resistor R3 appears as positiveand negative (or negative and positive)increments of voltage in series with the grid and plate voltage,supplies for the'braking field oscillation detector 5. -Sinee the platevoltcase tif the potential of only one' ofthe electrode elements of theBarkhausen oscillator is varied for frequency'control. IV have foundthatthe frequency of the Barkhausen oscillator 5 can be maintainedpractically constant with varying power supply, if the plate and gridthereof are arranged to take suitable proportional amounts of the powervoltage change and both in the same direction, Whether this change is ina positive ora negative direction. ,Y

Itis contemplated, inzaccordance with the invention, that anyone or allof the factors controlling the frequency of an ultra high frequencyoscillator may be used inthe automatic control of the frequencyincluding any other electrodes and the emission control of thecathode;For inling voltage is applied to a, special grid 28 placed between thecathode I0 and grid 3 of the tube 5 Y detector or its equivalent.

However, when. the intermediate frequencyV changes,V due to f anundesired change in the ieeilener of 'the'eilsheeeee eseilleier, the

and drawing no current.

It is 21150 contemplated in accordance with the invention, thatelectro-mechanical means may be used to control the tuning and/orvoltages of an ultra high frequency oscillator from a differential shownconventionally, in box form, means designated A for converting theoutputV of the diiferential detector to suitable electrical values whichare utilized by other means B in applying. frequency control to either atransmitting oscillator y or to the receiving ultra high frequencyoscillating detector. The means B may apply electrical control through amechanically driven voltage control system, or it may apply tuninglcontrol i by means of a mechanical, system, or it may appily magneticcontrol in either a mechanical, or

In Fig. 4, there is electrical manner. Fig. a. shows an arrangement forvachieving the results set forth in Fig. 4. In Fig. 5a, the differentialdirect current amplifier is replaced by a sensitive differential relay55, the relay tubes 5l are normally at plate current cut-off by means ofbias battery 52, A change of frequency causes relay 50 to short circuitthe bias on one of the tubes 5I which causes plate current to flow inthat tube, thus operating the electromechanical device 54 as follows.The rotating shaft 56 is driven continuously by motor 55 through theflexible coupling 51. Normally, the shaft rotates without touchingeither side of the groove in the wheel 58, in which case the frequencycontrolling condenser 59 is not moved. When plate current flows in oneof the relay tubes 5|, the armature 58 is pulled up or down accordingly,thus engaging one side of the groove in 58 and causing the condenser 59to be rotated in the proper direction to correct the frequency change.

It is further contemplated that the automatic control feature of theinvention for use with a Barkhausen or other type ultra high frequencyoscillator may be applied to the oscillator by the method of varying asuitable magnetic field placed in the region of the elements of thetube; such magnetic eld can be varied in amplitude and/or in itsrelative position by the means B in Fig. 4. Thus, mechanical control ofa magnetic eld may be had in Fig. 5a, for instance, by attaching amagnet to the shaft of 58 in place of condenser 58 so that the positionof the eld, or its strength, is changed by rotation of the shaft. Ifmagnetic control is really desired (which might be the case in magnetrontype oscillators), it might be preferable to use direct currentamplifier stages fed by the differential detector, in order to controlthe current in an electromagnet suitably placed near the oscillatortube. Such an arrangement in simple form is shown in Fig. 5b, theoperation of which will be evident from an inspection of the drawings.

If desired, the principles of the invention may be applied to an ultrahigh frequency transmitter, wherein the Barkhausen oscillating detectorof Figs. 1 and 2 is replaced by a suitable oscillating detector of knownstable frequency which is designed to have its frequency controlled, orby a Barkhausen oscillator of improved frequency stability; or it may bean ordinary rectifying detector in which the transmitter frequency and aknown stable frequency such as the harmonic of a crystal controlledoscillator may be combined to produce the intermediate frequency. Also,the control voltages or currents of the differential detector would beutilized to control the frequency of the transmitting oscillator whichmight be of the Barkhausen type which is controlled in the embodimentsdescribed, or any known oscillator subject to frequency control.

What is claimed is:

In an ultra short wave frequency-modulation receiver, a multi-electrodeBarkhausen oscillator coupled to a receiving antenna for beating withthe received signal to produce an intermediate frequency, anintermediate frequency amplifier, a detector coupled to the output ofsaid intermediate frequency amplifier, a direct current amplifier and alow pass audio frequency filter coupled to the output of said detector,and a cir-- cuit from said direct current amplifier to an electrode ofsaid oscillator for maintaining the frequency thereof at a steady valuediffering from that of the incoming wave by a predetermined amount,whereby only low frequency variations of the direct current voltage arepassed to said oscillator.

RALPH W. GEORGE.

